1. Field of the Invention
The present invention relates to digital modulation methods, digital demodulation methods, and prerecorded recording media which are suitable for use in, for example, digital versatile disks (hereinafter referred to as xe2x80x9cDVDsxe2x80x9d). More particularly, the present invention relates to a digital modulation method, a digital demodulation method, and a prerecorded recording medium capable of inserting arbitrary sub-information into serial data by controlling the conversion of actual-value digital data into serial data.
2. Description of the Related Art
For example, one type of apparatus for inserting arbitrary sub-information into serial data recorded in DVDs is described in U.S. Pat. No. 6,078,552 (Yamamoto et al.). According to this apparatus, arbitrary sub-information is inserted by modulating the light intensity of a laser beam when recording serial data on a DVD. When playing the DVD, the sub-information is extracted by detecting variations in the read levels of read signals.
The sub-information is used to prevent illegal disks created by copying and alteration, to determine whether or not playback is under copyright, and to determine whether or not copying is authorized/unauthorized. The above-described modulation of the light intensity of a laser beam, which is performed when recording data, is effective in optical recording media such as DVDs which employ light as read/write means. However, the modulation is ineffective for magnetic tapes and magnetic disks having recorded therein data created by copying or alteration.
When recording data on a CD-R (Compact Disk Recordable) or a CD-RW (Compact Disk Re-Writable), the above-described sub-information is recorded by a special mechanism for modulating the light intensity of a laser beam. It is thus difficult to perform the modulation method in consumer apparatuses. Specifically, it is impossible to achieve the foregoing modulation method for CD-Rs and the like. Therefore the modulation method is ineffective for recording data created by copying or alteration.
When recording digital data on a DVD, 8-bit digital data to be recorded (hereinafter xe2x80x9cdata-to-be-recordedxe2x80x9d is referred to as xe2x80x9ctarget dataxe2x80x9d) is converted into 16-bit serial data using the EEMplus (8-to-16 modulation) system, and recording signals are created using the NRZI (non-return-to-zero-inverted) system. At the same time, a digital sum value (hereinafter referred to as a xe2x80x9cDSVxe2x80x9d), which indicates the difference between the time for which the formed recording signals are at the value xe2x80x9c1xe2x80x9d and the time for which the signals are at the value xe2x80x9c0xe2x80x9d, is measured. The DSV can be obtained by linking xe2x80x9c1xe2x80x9d in the recording signals after the NRZI conversion to xe2x80x9c+1xe2x80x9d and xe2x80x9c0xe2x80x9d to xe2x80x9cxe2x88x921xe2x80x9d and computing the sum of 1xe2x80x2s (+1) and 0xe2x80x2s (xe2x88x921). When converting digital data into serial data, the serial data is selected so as to minimize the DSV.
Specifically, when the DSV is large, a signal component of the serial data leaks into a servo signal at a player side, and this results in servo instability. When the DSV is large in binarization of a read signal, the possibility of an error being caused in determining the slice level for the binarization is increased.
For 8-bit target digital data, 256 combinations are possible. For 16-bit data, 65536 combinations are possible. The EFMplus conversion is performed against a predetermined reference period T, and a row of bits for a period of 3T to 11T and 14T are used as serial data. A conversion table for converting 8-bit data into 16-bit data has states 1 to 4. On the basis of the states 1 to 4 and target digital data, serial data is generated.
For target digital data having the actual values xe2x80x9c0xe2x80x9d to xe2x80x9c87xe2x80x9d, the states 1 to 4 each have a main table and a sub table. The tables are arbitrarily selected, and serial data is generated. For target digital data having the actual values xe2x80x9c88xe2x80x9d to xe2x80x9c255xe2x80x9d, on condition that the state is either the state 1 or 4 and that a sequence of 0xe2x80x2s satisfies a predetermined value, the following data replacement is performed. Specifically, in the state 1, serial data in the state 4 can be replaced; in the state 4, serial data in the state 1 can be replaced.
The DSV can be controlled by controlling selection of main tables and sub tables for target digital data having the actual values xe2x80x9c0xe2x80x9d to xe2x80x9c87xe2x80x9d and by controlling data replacement in the state 1 or 4 of the target digital data having the actual values xe2x80x9c88xe2x80x9d to xe2x80x9c255xe2x80x9d. Generally, the DSV has been controlled so as to be minimized.
Specifically, when a DVD conversion table indicates that target digital data indicates xe2x80x9c0xe2x86x923xe2x86x920xe2x80x9d, there are eight possible patterns of serial data which can be output, as shown in FIG. 24. Also, there are eight possible combinations of state transitions. Referring to FIG. 24, each piece of serial data is shown such that the upper table is a main table and the lower table is a sub table. FIG. 25 shows variations of the DSV in this case. The terms xe2x80x9cmainxe2x80x9d and xe2x80x9csubxe2x80x9d indicate the history of table selections.
As has been described above, the DSV varies in accordance with, for example, the selection of tables. For example, the possibility of the final value ranges from a value close to the initial value to a value far from the initial value. The route between the initial value and the final value varies in accordance with, for example, the selection of tables. The DSV can be modulated in accordance with arbitrary sub-information, and the sub-information for preventing illegal disks and determining whether or not playback or copying is authorized can be inserted.
The DSV cannot be controlled for the entire target digital data. The DSV can be reliably controlled for the actual values xe2x80x9c0xe2x80x9d to xe2x80x9c87xe2x80x9d. It is not always possible to modulate the DSV in accordance with arbitrary sub-information. Since the DSV is arbitrarily changed for a signal which is not modulated in this manner, a signal similar to sub-information may be erroneously extracted from the signal, resulting in an incorrect determination or a malfunction.
A known method for modulating the light intensity of a laser beam is ineffective for recording media which do not use light. It is also difficult to provide a commercial recording apparatus with a function for modulating the light intensity of a laser beam. In a known system for modulating the DSV and inserting sub-information, satisfactory sub-information may not be inserted, and the possibility of malfunctioning cannot be eliminated.
In order to solve the foregoing problems, it is an object of the present invention to locally control a digital sum value (DSV) which indicates the difference between the time for which serial data signals are at the value xe2x80x9c1xe2x80x9d and the time for which the signals are at the value xe2x80x9c0xe2x80x9d, and to insert arbitrary sub-information using a variation pattern of the DSV. By setting the format of the variation pattern of the DSV, satisfactory sub-information can be inserted. By detecting the format of the variation pattern, possible incorrect determinations and malfunctions can be eliminated.
According to an aspect of the present invention, a digital modulation method for converting actual-value digital data into serial data is provided. The digital modulation method includes the steps of locally controlling a digital sum value (DSV) which indicates a difference between the time for which serial data signals are at the value xe2x80x9c1xe2x80x9d and the time for which the signals are at the value xe2x80x9c0xe2x80x9d; and inserting arbitrary sub-information using a variation pattern of the DSV.
According to another aspect of the present invention, a digital demodulation method for demodulating serial data into actual-value digital data is provided. The digital demodulation method includes the steps of measuring a digital sum value (DSV) which indicates a difference between the time for which serial data signals are at the value xe2x80x9c1xe2x80x9d and the time for which the signals are at the value xe2x80x9c0xe2x80x9d; and extracting arbitrary sub-information by detecting the variation pattern of the DSV.
According to another aspect of the present invention, a prerecorded recording medium having recorded therein serial data which is converted from actual-value digital data is provided. A digital sum value (DSV) which indicates a difference between the time for which serial data signals are at the value xe2x80x9c1xe2x80x9d and the time for which the signals are at the value xe2x80x9c0xe2x80x9d is locally controlled. Using a variation pattern of the DSV, arbitrary sub-information is inserted and recorded.